1. Field of the Invention
The invention relates generally to light guide plates and backlight modules adopting the same, and more particularly to a light guide plate typically used in liquid crystal display devices and a backlight module adopting the same.
2. Related Art
Liquid crystal display (LCD) devices have many excellent performance features, such as large-scale information display capability, low power consumption, easy coloring, long life, environmental soundness, and so on. Therefore, liquid crystal display devices are widely used in numerous applications. A typical liquid crystal display device generally includes a backlight module. The backlight module is used to convert linear light sources such as cold cathode ray tubes, or point light sources such as light emitting diodes, into area light sources having high uniformity and brightness.
Referring to FIG. 4, a conventional backlight module 10 includes a light guide plate 20, a reflector 30, a light source 40, and a cover 50. The light guide plate 20 includes an incidence surface 21, an emission surface 23 adjoining the incidence surface 21, and a bottom surface 22 adjoining the incidence surface 21 and being opposite to the emission surface 23. A plurality of refractive lenses 24 are formed on the emission surface 23, and each refractive lens 24 is a hemispherical dot. The reflector 30 is located below the bottom surface 22 of the light guide plate 20. Rear, top and bottom portions of the light source 40 are covered by the cover 50, which is positioned beside the incidence surface 21 of the light guide plate 20.
In use, incident light beams are emitted from the light source 40 and propagate into the light guide plate 20 via the incidence surface 21. The light guide plate 20 ensures that most of the light beams traveling therein can be emitted from the emission surface 23 thereof. The reflector 30 is used to reflect at least some and, preferably, nearly all of the light beams that are emitted from the bottom surface 22 back into the light guide plate 20. This reflection enhances the utilization ratio of the light beams.
However, light with a relatively long wavelength has a relatively small refraction angle, and is focused at a relatively far point when it travels through the refractive lenses 24. On the other hand, light with a relatively short wavelength has a relatively large refraction angle and is focused at a relatively near point when it travels through the refractive lenses 24. That is, the focus of blue light, the focus of green light and the focus of red light traveling through each refractive lens 24 are sequentially located on an axis of the refractive lens 24. Therefore, the emitted light beams generally cannot be converged via the refractive lenses 24. This causes chromatic aberration and reduces a brightness of the emitted light beams. Thus, the light guide plate 20 frequently cannot provide a satisfactory display quality.
What is needed, therefore, is a light guide plate that can provide emitted light beams with high brightness.
What is also needed is a backlight module adopting the above-mentioned light guide plate.